Color liquid crystal display projectors generate display images and project them onto display screens, typically for viewing by multiple persons or viewers. The display images may be formed by transmitting light from a high-intensity source of polychromatic or white light through an image-forming medium such as a liquid crystal display (LCD).
Conventional liquid crystal display systems include a mosaic of color selective filters positioned over the liquid crystal display element to separate the white light into its constituent color components (e.g. , red, green, and blue) to render a full color display. The mosaic of color filters is arranged to provide particular color light components to particular sub-element apertures of the picture elements or pixels in the display.
A disadvantage of such conventional liquid crystal display projection systems is that the mosaic of color selective filters blocks significant amounts of light. In projection display applications, light brightness is an important performance feature. To improve upon the light brightness capabilities of conventional liquid crystal display projection systems, various modifications have been developed.
U.S. Pat. No. 5,161,042 of Hamada describes a color liquid crystal display projection system that utilizes a sequence of red, green, and blue inclined dichroic color selective mirrors to efficiently form separate color component light beams. The separate color component light beams are directed to a microlens array that converges the light beams onto the picture element apertures of the liquid crystal display. While providing improved efficiency in the color separation of light over conventional color filter mosaics, the Hamada patent appears to employ conventional illumination components, which suffer from several systemic deficiencies.
Within the apparent context of conventional color filter mosaic liquid crystal display systems, U.S. Pat. No. 5,455,694 of Ariki et al. describes an illumination optical system that includes a microlens array positioned near the liquid crystal display elements to provide them with a high aperture ratio. The illumination optical system is constructed so that the light source is effectively conducted to the picture elements or pixels and is "almost not eclipsed" by optically opaque components of the pixels. Despite such an improvement, the Ariki et al. patent also utilizes conventional optical illumination compounds or arrangements that hamper the overall illumination for efficiency.
Illumination brightness in color of LCD projection display is an important performance feature. As illustrated by the Hamada and Ariki et al. patents, typical attempts at improving illumination brightness focus on localized optical components. An aspect of the present intention is that illumination brightness in a color LCD projection system is addressed at a systemic level.
Accordingly, the present intention includes a color liquid crystal display projector having a light source with a radiating element (e.g., arc or incandescent) and a liquid crystal display (LCD). The LCD includes an array of multiple picture elements or pixels that each have separate color component elements. A microlens array is positioned adjacent to the liquid crystal display to direct light from the light source into the picture elements.
Illumination imaging components cooperate with the microlens array to image the radiating element toward the separate color component elements of the liquid crystal display. Multiple differently inclined dichroic mirrors (e.g., blue, red and green in sequence) split the light into light beams of different color components that are imaged onto the appropriate color component elements of the liquid crystal display.
In one embodiment, the illumination imaging components include a hemispherical reflector with the radiating element or arc of the the light source positioned generally at the focal point of the reflector. The hemispherical reflector may be separate from or integrated with the light source. For example, the light source may include a spherical envelope portion that contains the radiating element and a reflective coating that is directly on and partly covers the spherical portion. In another embodiment, a polarizing beam splitter provides high efficiency polarization of light directed to the LCD while also providing optical path length reduction due to a higher refractive index. The systemic utilization of illumination enhancing features cooperate to provide a brighter LCD projector. Increased brightness allows such projectors to be used under a wider variety of lighting and display conditions.